1. Technical Field
The present disclosure relates to semiconductor structures.
2. Description of Related Art
Semiconductor structures fabricated by gallium nitride for light sources, such as blue, green, and white light sources, have long lifetime, high energy conversion efficiency, and environmentally friendly. Therefore, the semiconductor structures are widely used as the light sources in large screen color display systems, automotive lightening, traffic lights, multimedia displays, optical communication systems, and so on.
A conventional semiconductor structure used as the light source includes an N-type semiconductor layer, a P-type semiconductor layer, and an active layer located between the N-type semiconductor layer and a P-type semiconductor layer. In an operation, a positive voltage and a negative voltage are applied respectively to the P-type semiconductor layer and the N-type semiconductor layer. Thus, holes in the P-type semiconductor layer and electrons in the N-type semiconductor layer can enter the active layer and combine with each other to emit visible light, and the visible light is emitted from the semiconductor structure. However, near field evanescent waves emitted from the active layer are internally reflected inside the semiconductor structure, so that a large portion of the light emitted from the active layer remain in the semiconductor structure, thereby degrading the light extraction efficiency.
What is needed, therefore, is to provide a semiconductor structure having a high light extraction efficiency.